JPS6312954B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stable gold alloy strike plating bath consisting of gold, tin and a third element.

Many alloy plating baths of gold and tin have been proposed. Most of these consist of gold as alkali cyanide, stannous ions, and complexing agents. However, gold and tin alloy plating baths have the disadvantage that it is difficult to obtain gloss, and stannous ions are easily oxidized to stannic ions, making them unstable as plating solutions.

The purpose of the present invention is to improve the above-mentioned drawbacks,
The object of the present invention is to provide a stable gold alloy plating bath for strikes based on metallic tin, which has excellent corrosion resistance and mechanical properties, and provides a glossy deposited film.
The gold alloy strike plating bath of the present invention is a gold alloy strike plating bath suitable for strike plating of gold alloys, in which the amount of gold added as gold potassium cyanide is 0.2 to 0.
0.8g/, and nickel as metal is 0.1~5g/
and 0.2 to 10 g of stannous, and 150 g of at least one compound that complexes the metal.
~750g/, the brightener is 0.2~30g/, and at least one of the stannous antioxidants is 0.5~750g/.
It is characterized by the addition of 50 g/day and a pH of 4 to 6.

The structure of the plating bath of the present invention is as follows.
The amount of gold added as gold potassium cyanide is
It is 0.2-0.8g/. If the amount of gold is less than 0.2 g/g, the gold is rapidly consumed by precipitation, and if it exceeds 0.8 g/g, the adhesion of the deposited film is poor. This improvement in adhesion is due to the following reasons. That is, although gold has a high deposition potential, complexing at a low concentration lowers the deposition potential and can prevent a substitution reaction that causes poor adhesion.

In reality, when copper or nickel plates are immersed in a bath containing 0.8 g or more of gold, gold will precipitate by displacement.

Next, the amount of stannous ions is 0.2-10 g/. If it is less than 0.2 g/l, the stannous ions will be severely consumed by plating, and if it exceeds 10 g/l, the amount of tin precipitated will be too large, which is undesirable because the corrosion resistance, which is the object of the present invention, will deteriorate.

Elements added to increase the mechanical strength of gold and tin alloys are group a, group a of the periodic table,
metals of group a, group a, group a, group a and b
Possible examples include those of the group B, group b, and group b. These elements precipitate in the gold-tin alloy and can significantly improve mechanical strength, especially hardness.
If two or more types are added, the effect will be even more synergistic. The aforementioned elements are, for example, titanium,
Niobium, molybdenum, rhenium, iron, nickel,
Cobalt, rhodium, palladium, copper, silver, silicon, phosphorus, etc. are conceivable, each being added in the form of a compound suitable for aqueous solution. Among these, nickel is the most suitable for three reasons: it is easy to add, it has mechanical strength, and it improves plating coverage. Of these, the nickel ion is 0.1
~5g/.

If the amount is more than 5g/, complexation is difficult;
Moreover, if it precipitates in large amounts, it will not serve the purpose of being an additive element, so it is not suitable. Moreover, if it is less than 0.1 g/g/m, the mechanical strength will not increase.

The amount of compounds complexing the above metals is 150-750
g/. If the amount is less than 150 g, the complexing effect will be small and the plating bath will lose its buffering effect, making the plating bath unstable. Moreover, if the amount is more than 750 g, the viscosity of the bath becomes high, which is not practical.
The more complexing agent there is, the more stable the plating bath will be, and at the same time, the higher the working current density will be, and the less change in the composition of the deposited alloy due to the current density will occur.

Desirable complex compounds include organic carboxylic acids such as malic acid, citric acid, gluconic acid, malonic acid, and maleic acid. This is because organic carboxylic acids have strong complexing and buffering effects, and can allow gold potassium cyanide to exist stably even on the acidic side.

The plating bath according to the present invention contains gelatin, toluidine, phenylacetamide, sodium arsenite,
At least one of the reaction products of β-naphthol, peptone and acetaldehyde with O-toluidine
Excellent shine can be obtained by adding seeds. The amount added is 0.2 to 30g/. 0.2
If it is less than 30g/, no gloss will be obtained, and if it exceeds 30g/, there will be no gloss effect and the plating solution will become unstable.
The effect of this brightener is particularly noticeable when the plating temperature is below 35°C. This is because tin cannot be deposited smoothly if the bath temperature is below 35°C.
Furthermore, these brighteners have little effect on the stability of the plating bath, the precipitation conditions, etc.

Generally, stannous ions are more easily oxidized to stannous ions, and this becomes more pronounced as the bath temperature is higher. Since stannic ions not only do not contribute to precipitation but also have a negative effect on uniform electrodeposition, it is a practically effective means to add an antioxidant to the plating bath. As antioxidants, hydrazine sulfate, hydroxylamine sulfate, L-ascorbic acid, P-
Cresolsulfonic acid, resorcinol, formalin, hydroquinone, sodium sorbate or glucose are effective. The amount added is 0.5 to 50g/. If it is less than 0.5g/, there is no antioxidant effect;
Even if the amount exceeds 50g, there will be no further effect and the glazing solution will become unstable. Furthermore, when two or more of these antioxidants are added, their effects appear synergistically, and the stability, gloss, precipitation conditions, etc. of the plating bath are not adversely affected.

The alloy composition to be deposited depends on the concentration of each metal ion in the bath, complex compound concentration, pH, bath temperature, and cathode current density. It is desirable that the concentration of gold and complex compound be as high as possible. This is because the larger the amount of gold and complex compound, the less the change in the deposited gold composition with respect to the current density, and once the bath composition is determined, the deposited alloy composition will be approximately constant.

Higher pH results in less tin electrodeposition, but improves the appearance of the precipitates. If the pH is on the alkaline side, stannous ions become unstable, so the pH of the bath should be 4 to 6.
Preferably it is 4.5±0.5.

If the PH is less than 4, gold potassium cyanide is decomposed and the PH
When it exceeds 6, stannous is decomposed. Bath temperature is 15
It can be used at temperatures up to 90°C, and the higher the temperature, the better the plating appearance and the faster the precipitation rate, but the more the brightener and antioxidant are consumed, so the appropriate bath temperature must be determined.

The practical range of cathode current density is 0.1 to 10 A/dm ² .

The anode used in this plating bath is platinum, carbon,
Titanium platinum and titanium rhodium are preferable. Also,
It is desirable that the surface area ratio of the anode to the cathode is two times or more. Further, by sufficiently stirring this plating bath, the appearance and uniformity of the precipitated alloy will be improved. As a stirring method, cathode locking, jet flow, or a combination thereof is recommended; air stirring should not be used.

Next, embodiments of the present invention will be described.

Example 1 Gold (as gold potassium cyanide) 0.8g / Tin (as stannous sulfate) 2g / Nickel (as nickel sulfate) 1g / Malic acid 300g / Hydrazine sulfate 30g / Gelatin 1g / Peptone 0.5g / PH 4.5 bath Temperature: 20°C Cathode current density: 1A/dm ² anodes Carbon plating time: 5 minutes When plating was performed with stirring under the above plating bath composition and plating conditions, the results were 85% gold and tin.
A glossy deposited film containing 14.8% nickel and 0.2% nickel and a thickness of 0.5 μm was obtained.

The embodiments described above are part of the invention and are not intended to limit the invention.

Next, the effects obtained by the present invention will be listed below.

(1) Since the plating solution is stable and the precipitated plating becomes dense, it is possible to provide strike plating as a base for gold alloy plating with excellent adhesion.

A plating film with excellent adhesion can be obtained due to the low concentration of metal ions and high current density.

(2) Excellent gloss can be obtained.

(3) Hardness is increased by adding a third element to the gold-tin alloy, so a hard film can be provided as a base layer, and the top plating can be arbitrarily selected.

(4) Since the precipitated alloy composition can be freely changed by changing the bath composition and current density, there is no need to change the bath composition every time the top plating changes.

(5) Good corrosion resistance of the deposited film.

(6) Excellent precipitates can be obtained even at room temperature.

(7) Metsuki bath is stable.

The plating bath according to the present invention exhibits remarkable effects as described above.

Possible uses for this plating bath include the following:

(a) It has a wide range of applications, especially for underlay plating. Furthermore, it may be used as is, depending on the purpose.

(b) White decorative plating with high hardness Specifically, it can be used for strike plating of ornaments, watch cases, eyeglass frames, etc. that require excellent appearance, hardness, and corrosion resistance.

(c) Plating for electrical contacts Because it has excellent wear resistance, corrosion resistance, and conductivity, it can be used for electrical contacts.

(d) Plating for IC bonding When an appropriate amount of tin is added to gold, the melting point is significantly lowered, which can be used to plate lead frames for IC wire bonding.

As described above, the gold alloy strike plating bath according to the present invention can be used for various purposes such as decoration, contacts, and bonding, and is therefore an extremely useful invention in practice.

Claims (1)

[Claims] 1. In a gold alloy strike plating bath suitable for strike plating of gold alloys, the amount of gold added as potassium gold cyanide is from 0.2 to
0.8g/, and nickel as metal is 0.1~5g/
and 0.2 to 10 g of stannous, and 150 g of at least one compound that complexes the metal.
~750g/, the brightener is 0.2~30g/, and at least one of the stannous antioxidants is 0.5~750g/.
A gold alloy strike plating bath characterized by adding 50 g/g/g of gold and having a pH of 4 to 6.